The present invention relates to the variable attachment of a front derailleur to a braze-on mounting socket of a bicycle frame.
A typical braze-on mounting socket is located on the seat tube of the bicycle frame oriented towards the axis of the crank assembly and located at a defined distance from the axis of the crank assembly. This defined distance is determined by the type of chainrings being used, e.g. a standard set of chainrings with 53/52 or 53/30 teeth, or a compact set of chainrings having 50/36 and 48/34 teeth. A drawback associated with the braze-on mounting socket is that it does not accommodate for the radial difference between different sets of chainrings requiring the use of two different front derailleurs to compensate for the radial difference.
EP 0 757 952 A1 discloses a front derailleur including an attachment device for fastening the derailleur to the crank assembly which accommodates different sized sets of chainrings. The attachment device includes a frame, a chain cage, and two adjusting bushings, each having one eccentrically oriented opening, which may be mounted in two positions thus allowing for different radial distances between the front derailleur and the axis of the crank assembly. The adjustment range that results from the variable installation of the adjusting bushings, corresponds to the radial difference between the large chainrings of the different sets of chainrings. This attachment device allows the front derailleur to be mounted to the crank independently of the position of the braze-on mounting socket. However, in comparison to a conventional attachment to a braze-on mounting socket, this configuration requires a complex frame support and two adjusting bushings. This negatively affects the installation time and production costs.